Florestas estacionais e áreas de ecótono no estado do Tocantins, Brasil: Parâmetros estruturais, classificação das fitofisionomias florestais e subsídios para conservação

Abstract

The purpose of this study was to describe the richness, structure and diversity of tree species occurring in seasonally dry forests and some ecotone areas (Seasonal Forest/Ombrophilous Forest) in the state of Tocantins (Brazil). We aimed to provide information for conservation, management, environmental compensation and restoration strategies, and discuss their phytogeography identities in relation to other Brazilian forests. We selected 22 areas in 18 hydrogeographic basins and performed an inventory of all trees species (DHB > 5 cm) occurring in 477 plots of 400 m2. We conducted a classification analysis of the vegetation using the TWINSPAN method in two different scales. The first assessed the beta diversity among plots within the state of Tocantins, and the second analysed similarities between these forests and other forests ecosystems in the Cerrado ecoregion and related ecotones in Central Brazil. A wide variation of species richness (33 to 243 species), density (486 to 1179 trees.ha-1), basal area (14.04 to 37.49 m2. ha-1), diversity indexes (H' = 2.75 to 4.59) and evenness (J' = 0.72 to 0.86) across the sites was found. Based on floristic and structural aspects, classification analyses identified four major forests types: Seasonal Deciduous Forest, Seasonal Semi-deciduous Forest, and two ecotones Seasonal Semideciduous Forest/Ombrophilous Forest and ecotone Seasonal Deciduous Forest / Ombrophilous Forest. In order to maintain plant and habitat diversity in the Amazon/Cerrado transition zone, the creation of conservation areas should be intensified using biogeographical patterns as site selection criteria.